FUSION - PowerPoint PPT Presentation

FUSION. Michael Schantz , Lorenzo Tulipano Phys 43, SRJC 12 May 2009. Is nuclear power the answer?. Transportation contributes to over 50% of CO 2 emissions, but nuclear power cannot directly reduce this. There are no direct greenhouse gas emissions from nuclear power.

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FUSION

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Is nuclear power the answer? • Transportation contributes to over 50% of CO2 emissions, but nuclear power cannot directly reduce this. • There are no direct greenhouse gas emissions from nuclear power. Could the Ford Fusion be powered one day by… fusion? Photo courtesy of Ford Motor Company

Fusion in the Sun • Every star produces energy through fusion. • About 90% of the stars use hydrogen, the rest use other heavier elements. • Two conditions must be met: - A high temperature must be sustained. • - The density of nuclei must be high enough in order to guarantee a high rate of collisions. • The sun uses the Proton-Proton Cycle: • - It is believed that a series of three nuclear reactions occur in the Sun. • - The Sun releases energy as gamma rays, positrons, and neutrinos. 1. 2. 3. Photo courtesy of NASA Goddard Laboratory for Atmospheres

Fusion in a Reactor • A mixture of hydrogen atoms (deuterium and tritium) are heated to the point where they collide and spontaneously fuse together. • This reaction produces large amounts of thermal energy, which can be converted into electricity. • The reaction is shown below:

Raw Materials & Availability • Deuterium • Also known as heavy hydrogen, deuterium is naturally abundant in our oceans. • There is approximately 1 deuterium atom for every 6500 hydrogen atoms in ordinary seawater. • Tritium • Tritium is extremely rare on Earth, so it must be produced from lithium. • Lithium-6 must be used to create tritium, which exists as about 7.5% of the lithium on Earth. The reaction to convert lithium-7 is unfavorable. • Lithium is found in rocks on the Earth’s surface, but at a concentration of about 20-70 ppm. • Although lithium makes a small amount of the earth’s crust, it would take millennia to exhaust all of the earth’s crust. • The process for turning lithium-6 into tritium is as follows:

Reactors Tokamak • A tokamak fusion reactor is designed in a toroidal shape. • During the fusion process, deuterium and tritium are held in the plasma state, above 100 million Kelvin. • A magnetic field is used to contain the plasma. • Fast neutrons shoot out of the plasma and must be absorbed by the tokamak walls. • Currently, the Join European Torus (JET) is the largest operating tokamak reactor, producing 16 MW (thermal), which is 70% of the required power to initiate the reaction. • JET can only maintain its peak power production for less than a second. Photo courtesy of http://www.plasma.inpe.br

Reactors ITER • The International Thermonuclear Experimental Reactor (ITER) is the next generation of the tokamak design, and it is being built in southern France. • ITER has been designed to produce 500 MW of thermal power for up to 1,000 seconds. • It is expected that ITER will produce 5-10 times more thermal power than required to heat up the plasma. • This new reactor will be completed in 2014 and will run experiments for 20 years. Photo courtesy of http://ec.europa.eu

Reactors Stellarator • Similar to the tokamak, stellarators use a toroid bent into a figure eight shape. • Stellarators, unlike tokamaks, do not require a toroidal current so that the expense and complexity of current drive can be avoided. • There also is no risk of current disruptions. • It might be possible to use the additional degrees of freedom to optimize a stellarator in ways that are not possible with tokamaks. • Transport in stellarators tends to be higher than tokamaks because the changes in magnetic field strength is greater in stellarators. Photo courtesy of http://www.ipp.mpg.de

Reactors NIF • The National Ignition Facility (NIF) uses an inertial confinement fusion (ICF) device powered by 500 terawatt (TW) lasers to heat and fuse deuterium and tritium together. • It was certified complete by the U.S. Department of Energy on 31 March 2009. • This is the largest ICF device ever built and has the potential to produce more energy than it consumes (“ignition”). • If NIF can reach ignition, the initial fusion reaction will release enough energy to ignite the surrounding fuel, thus sustaining a chain of fusion reactions without additional energy input. • An additional goal for NIF is to reduce the cool down time between reactions to 5 hours so that it can be fired up to 700 times a year. Photo courtesy of U.S. Gov. – Public Domain

Problems • Scientists are not able to contain a fusion reaction long enough for there to be a net gain in energy. • It is currently estimated that it will take 50 years for fusion energy to be commercially produced. • Tremendous costs: • Tritium costs about $200 million per kg. • ITER will require 28 kg per year for research. • While the deuterium is stable, tritium is radioactive and has a half life of about 12.33 years. The beta radiation produced by its decay cannot penetrate human skin, but a loss of tritium means higher costs.

Cost of Fusion On average, over the past 50 years, the U.S. has had a budget of $250 million for fusion energy development/research per year. So far, nearly $13 billion has been spent on fusion energy in the U.S. U.S. Budget for Fusion Energy (dollars in thousands) User Facility Operations ITER Total Estimated Cost Research Total Source: U.S. Department of Energy

Conclusion As of right now, fusion reactors are net consumers of energy, but if new reactors such as NIF or ITER can become net producers of energy, then nuclear fusion will be a viable replacement for coal and gas fired power plants. It may not be the long term solution, but hopefully it can help us transition to the New Energy Era (2080 and beyond).